This invention is concerned with a brake system eg for a vehicle.
Many vehicles are equipped with disc brakes to fulfil the primary braking function of stopping or slowing the vehicle. Such disc brakes are often operated by a foot pedal and hence do not operate in the absence of the driver. For this reason, the vehicles are equipped with a parking brake which can be held in a xe2x80x9cbrakes onxe2x80x9d condition in the absence of the driver, the parking brake serving to prevent the vehicle from moving from rest. Conventionally, such parking brakes are of the drum brake type, comprising a hollow cylindrical drum and two xe2x80x9cshoesxe2x80x9d comprising friction material. The shoes are mechanically-operated to engage the inner cylindrical surface of the drum with a braking force. Thus, the overall brake system has a considerable weight.
It is common for the disc of a disc brake to be the so-called xe2x80x9ctop-hatxe2x80x9d type comprising an annular inner portion which is bolted to a hub, a joining portion which is generally cylindrical and extends axially of the hub, and an annular friction material-engaging portion joined to the inner portion by the joining portion. In order to save weight, the interior surface of the joining portion is often utilised as the drum of a drum type parking brake, thereby eliminating the necessity for a separate drum. However, where the disc is not of the top-hat type, this solution is not available.
GB 2031538 A, in connection with FIG. 4 thereof, discloses a brake of the enclosed type suitable for use in the agricultural or construction industries. This brake has a hollow cylindrical hub portion of relatively small diameter which provides a mounting for a disc of a disc brake. Axially spaced from but integral with said hub portion is a further hollow cylindrical hub portion of much greater diameter which serves as the drum of a drum parking brake. Thus, the disc mounting and the drum are provided by different portions of the hub.
In WO 98/25804, a disc brake is described in which at least one disc is mounted on a hub. The disc is mounted on the hub by means of mounting means arranged so that the hub and the disc rotate about the central axis of the hub as a unit but the disc can perform axial sliding movement on the hub. The specific example given in WO 98/25804 has two discs mounted on the same hub, both being slidable axially. The brake also comprises a piston and cylinder assembly having its cylinder fixed relative to a suspension link of a vehicle, the cylinder being integrally formed with the link. The system also comprises a caliper fixed relative to the cylinder, the caliper providing supports for friction pads of the system, including pads between the two discs. The pad furthest from the assembly is fixed to the caliper but the remaining pads are slidably mounted thereon. When the piston and cylinder assembly is operated, the pad operated upon by the assembly and the pads between the discs slide on the caliper, and the discs slide on the hub until each disc is engaged on both sides by a pad.
The disc brake of WO 98/25804 operates on a hub which comprises a mounting portion on which the discs are mounted. The mounting portion is generally in the shape of a hollow cylinder, the discs being mounted on the outer cylindrical surface thereof. The disc brake is for a driven hub and the interior of the mounting portion is occupied by a connection between the hub and a drive shaft.
It is an object of the present invention to provide a brake system of the general type disclosed in WO 98/25804, the system being of reduced weight.
The invention provides a brake system comprising a disc brake, a drum brake, and a hub arranged to rotate about a central axis thereof, the hub comprising a mounting portion generally having the shape of a hollow cylinder centred on said axis, the disc brake comprising a disc mounted on an outer surface of said mounting portion of the hub for rotation with the hub, the disc also being mounted for axial sliding movement on the hub, characterised in that the drum brake comprises friction material shoes which are moveable into engagement with an internal cylindrical surface of said mounting portion of the hub to act as a parking brake.
In a brake system according to the invention, the same hollow cylindrical portion of the hub is utilised both as the mounting portion of the disc of a disc brake and also as the drum of a drum brake, thereby avoiding the necessity for a separate drum or drum portion, giving a lighter, simpler and more compact brake.
There now follows a detailed description, to be read with reference to the accompanying drawings, of a brake system which is illustrative of the invention.